Hydrothermally processed polyethylene as starting point for fermentative production of triglycerides

Plastic waste accumulation in the environment is an exponentially growing problem that needs to be urgently addressed to avoid the catastrophic damage of terrestrial and oceanic ecosystems. In this work, currently undervalued plastic carbon content was aimed to be exploited by converting it into triglycerides (TGs), following a two-stage approach. Polyethylene (PE) was first treated by hydrothermal processing (HTP) to obtain PE oils that were later used as carbon source for fermentation with Yarrowia lipolytica and transformed into TGs. HTP PE oil obtained at 425ºC for 120 min was found as an optimal carbon source for the biotechnological stage. Under these optimized conditions, 75% of PE mass was transformed into a PE oil that could be used by Yarrowia as carbon source to grow and produce TGs. An oil concentration of 15 g/l in fermentation media in the biotechnological stage improved fermentation performance as well in comparison to 10 g/l concentration: biomass growth and TGs production yield were increased by 130% regarding the control. Thereby, an alternative approach towards turning one of the most widespread plastics as PE into TGs is proposed in this work.